1. Field of the Invention
This invention relates to a Ti-W sputtering target and a method of manufacturing such a target. More particularly, the invention relates to a Ti-W sputtering target having a high density and improved properties for forming thin films for electrodes or wiring members of semiconductor devices.
2. Description of the Related Art
Sputtering is a known method suitable for forming metallic thin films for electrodes or wiring of semiconductor devices. In sputtering methods, ions are caused to collide against a target to release metal therefrom which deposits as a thin film on a substrate adjacent to the target. Therefore, the properties of the metallic film formed by sputtering greatly depend upon the characteristics of the target.
In conventional sputtering processes, particles sized from 0.7 .mu.m to 10 .mu.m are produced from the target and enter the thin films. The particles cause short circuits or defective wires and as a result the registration rates of the semiconductor devices are substantially decreased. The sputtering target of the invention is desirable because it does not produce such particles.
Conventional Ti-W sputtering targets are made by a powder metallurgy (P/M) method, i.e., Ti powder and W powder are mixed and then sintered to high density under specific temperature and pressure conditions.
However, a Ti-W target made by the conventional P/M method uses relatively large sized Ti and W powder particles. As a result, there is a large difference between the crystal sizes of the constituent W-phase and Ti-W phase formed by the diffusion of Ti and W (hereinafter, "Ti-W phase"). When the crystal structures of the phases are large, non-uniform quality targets tend to be formed. Large particle sizes also may not sinter to high density. Therefore, when such nonuniform quality targets are used, uniform quality thin films having uniform compositions or thickness are difficult to obtain.
Furthermore, the conventional targets have low sinterability. Thus, they have low strength, and the weak intergranular material of the target tends to be broken down by the thermal stresses created by the sputtering process. As a result, the energy of the ions produces a large number of particles. Because Ti has a very high activity, it is easily oxidized to form an oxide. The Ti oxide forms a weakly bonded portion of the metal particles in the target and voids or pores are created. The voids or pores cause an increase in the impurity gasses in the target, an increase in the porosity, and a decrease in density. As a result, the number of particles created is increased during the forming of the films by sputtering. The semiconductor devices are contaminated by the particles or impurities mixed into the metal films, and the productivity is decreased.
When carbon or oxygen are introduced into the target from the Ti or W powder, problems are created. At those portions of the target which include significant amounts of carbon, the sputtering ions are insufficiently filliped which leads to the production of particles. The metal films including large amounts of carbon are difficult to etch and are susceptible to wiring breakage. The oxygen present in the material powder causes an increase of particle production, and the oxygen present in the metal films causes an increase in electrical resistance.
Even for high density targets having a density ratio of 0.99, it was also confirmed that the number of particles generated tends to increase due to the effect of impurities, and nonusable products are likely to increase when wiring patterns are formed by etching the contaminated thin films.